matthew@seymour:~$ ssh -p 2224 remote_host_name_or_IPIPv6 Basics
Much of what this chapter discusses is valid regardless of whether you are
using IPv4 or IPv6. We start here with a short description of each to lay a
foundation for further understanding. As IPv6 receives greater acceptance and
use, this understanding should be adequate to help you transition between the
two, even if specific issues are not addressed in the chapter. If you missed the
“Limits of IPv4 Addressing” note in the earlier “TCP/IP Addressing” section,
you should go back and read through it to get started.
IPv4 is based on 32-bit numbering, which limits the number of available IP
addresses to about 4.1 billion. This and how those addresses were assigned
have led to the realization that there are not enough IPv4 addresses available
for the number of devices that need IP addresses. This problem, noticed in the
1990s, is only one of the problems with IPv4. Others include large routing
tables, which are lists of the routes to particular network destinations, and
sometimes the network distances and topography associated with those
routes. These tables are stored in routers and networked computers.
To deal with these issues, IPv6 uses 128-bit numbering that can theoretically
allow well over 340,282,366,920,938,463,463,374,607,431,768,211,456 IP
addresses, which is normally expressed in scientific notation as about 3.4 ×
1038 addresses. That’s about 340 trillion, trillion, trillion addresses, meaning
we are unlikely to run out again anytime soon. This number of addresses
allows for each computer to have its own globally routable address. We don’t
need NAT in IPv6 to translate IP addresses as packets pass through a routing
device, as there are an adequate number of addresses available. IPv6 allows
us to go back to the easier-to-configure peer-to-peer style of Internet
networking originally conceived of and used in the 1980s. This creates
routing tables that are much smaller because fewer subroutes need to be
generated.
Some other useful features of IPv6 include the following:
Address autoconfiguration (RFC2462)
Anycast addresses (“one-out-of-many”)
Mandatory multicast addresses
IPsec (IP Security)
Simplified header structure